4BSD/usr/man/man5/dir.5

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.TH DIR 5 
.SH NAME
dir \- format of directories
.SH SYNOPSIS
.B #include <sys/types.h>
.br
.B #include <sys/dir.h>
.SH DESCRIPTION
A directory
behaves exactly like an ordinary file, save that no
user may write into a directory.
The fact that a file is a directory is indicated by
a bit in the flag word of its i-node entry;
see
.IR filsys (5).
The structure of a directory entry as given in the
include file is:
.RS
.ta 8n +10n
.PP
.nf
#ifndef	DIRSIZ
#define	DIRSIZ	14
#endif
struct	direct
{
	ino_t	d_ino;
	char	d_name[DIRSIZ];
};
.fi
.RE
.PP
By convention, the first two entries in each directory
are for `\fB.\fR' and `\fB..\fR'.  The first is an entry for the
directory itself.  The second is for the parent
directory.
The meaning of `\fB..\fR' is modified for the root directory
of the master file system
.RB (\*(lq / \*(rq),
where `\fB..\fR' has the
same meaning as `\fB.\fR'.
.SH "SEE ALSO"
filsys(5)